Controlling Weeds in Landscaped Beds Without Glyphosate (Widely Used Nonselective Herbicide)

Summary

• Glyphosate is an active ingredient in the nonselective herbicide formulation formerly associated with the brand name of Roundup^®. Now Roundup^® trade names may include different active ingredients.
• Due to human safety and other issues, users of these herbicides containing glyphosate are looking for alternative weed management methods and herbicides to control weeds.
• Other suitable herbicides and organic-based materials will control weeds in the landscape but require correctly timed applications.
• These alternative herbicides must be used in conjunction with other weed control strategies, such as applying weed-free mulch and physically removing weeds.
• Controlling weeds in the landscape without glyphosate will require a weed management strategy that may include routine mulch replacement, preemergent herbicides to reduce the weed seed germination, and hand removal to prevent weeds from going to seed.
• Perennial weeds, such as nutsedges, common bermudagrass, bahiagrass, and perennial viny species (kudzu, green briar, etc.) will be more difficult to control with these alternate herbicides.
• Timely applications of a nonselective herbicide to control small weeds may also be necessary.

Introduction

Glyphosate is the most widely used herbicide to control weeds in the landscape, according to the US Environmental Protection Agency¹. With an increasing concern about the human safety of glyphosate, there is a growing demand for alternatives to glyphosate. While there is little scientific evidence that exposure to properly applied labeled pesticides is detrimental to human health, there is a great deal of interest in reducing or eliminating all herbicide applications around the home landscape. For information about controlling weeds in the landscape without herbicides, see HGIC 2337, Weed Control on Landscapes: Non-Chemical Measures.

Weed Types

Weeds have different growth cycles. Summer annual weeds, such as crabgrass and purslane, emerge in the spring and early summer, flower, and set seed before the onset of cool fall weather and die. Winter annuals such as chickweed and annual bluegrass emerge in the fall or early spring, set seed before hot weather arrives, and die. These annuals reproduce by seeds, so preventing seed formation and dispersal will effectively reduce these problem weeds. Apply mulch before peak weed seed germination and emergence in early spring, mid-summer and fall; this will keep weeds from emerging and becoming established. Prior to applying mulch, hand pull or kill existing weeds.

Perennial weeds primarily grow either in the summer, such as yellow nutsedge and bermudagrass, or in winter, such as Florida betony and dandelion. These weeds reproduce by seed and underground perennial parts that include tubers, rhizomes, or bulbs. Perennial weeds are generally more difficult to control because of their persistent underground reproductive structures. Mulch is generally not as effective in controlling perennial weeds that grow from underground perennial parts. It is more effective to remove the underground parts of perennial weeds as much as possible before applying mulch. Mulch reduces perennial weed seed emergence.

Organic Mulches

Weed-free mulches prevent many weed seedlings from emerging and becoming established and serve as the foundation for effective weed control programs in the landscape. When using organic mulches, such as ground bark or pine straw, a 2-to-4-inch layer prevents weed emergence and growth. The depth of the mulch depends on the particle size, mulch type, and weed pressure. Organic mulches also reduce and buffer soil temperature, decreasing the maximum temperatures at the soil surface compared to bare ground. For more information on mulching, see HGIC 1604, Mulching.

Organic Herbicides

Although organic herbicides are produced from naturally occurring ingredients, many can pose a health hazard if used incorrectly and not according to label directions. Liquid organic herbicide sprays often contain strong acids, and whether the landscape bed is being treated with an organic or synthetic (non-organic) herbicide, follow all precautions on the label.

Table 1. Organic Herbicide Products *

Non-Herbicide Controls: Even in a setting where herbicides are used, non-herbicide weed controls are important for managing weeds and reducing chemical use. These controls focus on interrupting the weed life cycle and preventing them from becoming established.

Heat-based techniques effectively control broadleaf weed species, and several new technologies have been developed to make this available to homeowners. Heat controls involve applying a flame or hot steam to kill small weeds, which can be especially effective in gravel or cement driveways. However, grasses and perennial weeds will only be damaged and not killed. These heat-based devices require fuel and/or water.

Weed-free pine straw.
Ted Whitwell, ©2024, Clemson Extension

Bark mulch.
Ted Whitwell, ©2024, Clemson Extension

Weed-free pine straw (left) or bark mulch (right) suppresses weed emergence and growth by limiting sunlight from reaching the soil surface, reducing weed seed germination.

Non-organic Herbicides: Chemical Weed Control without glyphosate-type herbicides: Not using glyphosate does not mean not using herbicides altogether. Other herbicide options are available to maintain a weed-free landscape without glyphosate.

Preemergent Herbicides: Preemergent herbicides may be unnecessary in landscape beds where annual weeds have not been a major problem. Weed-free mulch may provide adequate weed control without a preemergent herbicide but may require occasional hand-weeding.

Using a preemergent herbicide in combination with weed-free mulch will reduce the number of annual weeds present in the landscape and potentially eliminate the need for other weed control measures. Many forms of preemergent herbicides are available, including granular formulations that are easy to apply. A preemergent herbicide must be applied before the weeds emerge.

Apply preemergent herbicides on top of the mulch to kill weed seeds in the mulch. If some weeds escape, consider hand-weeding, making sure to remove them before they produce seeds. Remove these weeds from the landscape because some can still produce seed even after they are pulled up.

Apply preemergent herbicides a few days before weeds are expected to germinate and appear. Time the granular or spray herbicide applications based on changes in the weather, such as a period of warm days, which will encourage warm season weeds to germinate. Preemergent herbicides are not effective on perennial weeds growing from underground reproductive structures. For more details on the preemergent herbicides available and how to use them, see HGIC 2335, Weed Control in Landscapes: Herbicides.

Post-emergent Herbicides

Apply nonselective postemergence herbicide sprays to small weeds like these young carpetweed seedlings.
Ted Whitwell ©2024, Clemson Extension

Post-emergent herbicides are applied as a spray after the weeds appear. The timing is especially important with post-emergent herbicides because large, mature weeds are significantly harder to kill. Apply within one to two weeks of weed emergence to prevent them from becoming established. If weeds are allowed to grow for too long, herbicides may not control them completely, leaving behind plant parts in the soil that may regrow.

Applicators need to know the best time to spray nonselective post-emergent herbicides, especially those without glyphosate. Inspect the landscape beds for emerged weeds and apply these herbicides when the weeds are young and small, less than 2 inches tall.

Nonselective Herbicides: Nonselective herbicides will damage any plant it contacts. Therefore, use the appropriate dosage and spray the weeds directly to avoid damaging desirable landscape plants. With any herbicide, be aware of the weather conditions. Windy conditions can increase the amount of drift. Consider spraying with a protective shield, such as an empty plastic container, to prevent spray droplets from contacting desirable plants. Read the label, which often contains additional instructions to help prevent the unintentional drift of herbicides. Nonselective herbicides will not effectively control turfgrass encroachment into landscape beds.

Large shepherd’s purse.
Ted Whitwell, ©2024, Clemson Extension

Common chickweed.
Ted Whitwell, ©2024, Clemson Extension

When nonselective herbicides are used on large weeds, they may not provide effective control, as illustrated by these pictures of diquat sprayed on a large shepherd’s purse (left) and common chickweed (right).

Table 2. Nonselective Herbicide Products*

*Common herbicide names are the generic form of the active chemical, while product names are the brand name of the chemical purchased.

Selective Herbicides: Selective herbicides are chemicals that only manage specific weeds. These herbicides are safe to use around desirable plants that are listed on the herbicide label. Selective herbicides are practical for controlling weeds in densely populated landscape beds. Depending on the specific herbicide, they will control specific weeds based on the active ingredients. Some consumer products will contain a mixture of active ingredients that can affect a wider variety of weeds. Read the label, spray at the right time, and avoid misapplications to sensitive landscape plants, namely ornamental grasses.

Controlling Grasses and Sedges: Weedy perennial grasses and encroaching turfgrasses are some of the most difficult weeds to control. Several herbicides are available that will effectively control grasses while leaving many other desirable plants untouched. However, proper identification is required to determine if the weed is a grass, sedge, or broadleaf weed. Sedges may appear like a grassy weed at first glance; however, they can be distinguished by a distinct triangular stem shape, whereas, by comparison, grass stems are typically circular and hollow.

Sedges and grasses will not respond to the same herbicides; therefore, properly identify these weeds before spraying. Additionally, the herbicides effective on grasses can take up to a week before injury symptoms appear. Never apply more than the recommended dose of any pesticide. Perennial grasses and nutsedges may require more than one herbicide application. They may regrow later in the summer but should be less vigorous and might need to be removed by hand.

Table 3. Selective Herbicides for Controlling Grasses and Sedges in Landscaped Beds*

Controlling Perennial Vines and Tree Seedlings

Perennial vines and tree seedlings are the most difficult plants to control in the landscape. Continually cutting the plants off at the soil surface will eventually control them. Brush control products containing triclopyr, such as Bioadvanced Brush Killer Plus^® or Ortho Max Poison Ivy Killer^®, will control these difficult-to-control plants but may require repeated applications. They may eventually have to be removed by hand.

Summary: For effective weed control in the landscape, start with a 2-to-3-inch layer of weed-free mulch. Organic herbicides or heat-based control techniques will control small weeds. Other control measures include applying a preemergent herbicide before the weeds emerge, followed by hand-weeding, or applying nonselective or selective herbicides when needed to control the weeds. Read the herbicide labels to apply the products correctly and safely. Remember, the label is the law. Perennial grasses, sedges, and vines are more difficult to control and will require careful herbicide selection and application according to label directions.

Source:

¹ EPA – Glyphosate Interim Registration Review Decision: Assessed 09/17/2024 – page 8, https://www.epa.gov/sites/default/files/2020-01/documents/glyphosate-interim-reg-review-decision-case-num-0178.pdf

Originally Published 10/24